1. Field of the Invention
The invention relates to a shaping shoulder as well as a device for producing longitudinally shaped webs having an open or closed cross-section and comprising at least one area inside the web in which the cross-section is curved outwardly. These are, for example, tubular film bags with longitudinal folds, tubular film bags with one or several chambers produced by dividing in the longitudinal direction, as well as longitudinally undulate webs.
2. Discussion of the Related Art
Longitudinally shaped webs are used inter alia in the packaging technology.
Generally known, employed in the packaging technology and, for example, used in horizontally or vertically operating tubular film bag machines, are shaping shoulders for shaping a plane web of a packaging material to a longitudinally shaped web, a prism which in the longitudinal direction is closed by an overlap seam or a fin seal. These closed prisms are called tubes. The removal of the plane web from the roll past the shaping shoulder is realized by removal members. They are positioned, viewed in the direction of movement of the web, behind the shaping shoulder. For closing the longitudinal seam, welding or sealing members such as welding bars or welding belts moving together with the tube are employed. After closing the longitudinal seam, a filling pipe projecting into the tube, for example, introduces the article to be packaged into the tube. Subsequently, a transverse sealing member or transverse welding member closes the bag wherein at the same time the bottom seam of the following bag is formed.
Shaping of the plane web to a prism-shaped cross-section is carried out essentially along a spatial line on the shaping shoulder, the so-called shaping edge. The area of the shaping shoulder from the planar intake of the web in the moving direction of the web extending farther to the shaping edge is referred to as the shoulder part; the area of the shaping edge to the exit of the tube is the prism part. The web contacts partially or entirely the surface of the shoulder and is curved by it in the direction to the shaping edge. Guiding of the web in the prism part is realized by the shaping edge as well as by the web removal member acting on the exterior of the tube and the shaping pipe in the interior of the tube. The shaping pipe can be at the same time the outer envelope of a feeding pipe.
The prisms or tubes have a multitude of cross-sectional shapes. They have in common that they are always curved inwardly about the entire periphery, i.e., that their inner angle is always smaller or identical to 180 degrees. Viewed in the moving direction of the web, the shaping edge, beginning at the point of the first shaping of the web toward the web edge is curved always with increasing or continuous slant in the direction of the exit of the tube, i.e., the curvature of the shaping edge is oriented toward the end of the tube. The shoulder surface which belongs to the shaping edge is defined by a set of straight lines beginning at the shaping edge and extending to the web edge (DE 237 289, DE 195 39 830). This surface is always curved beginning at the intake of the web in the direction of the exit of the tube.
The shaping of the shaping shoulder must be planar, i.e., the surface of the shaping shoulder must be designed such that it can be developed in a plane (DD 237 289, DD 147 652). This is the prerequisite for shaping the web without forming wrinkles or producing tears.
U.S. Pat. No. 4,514,965 describes a device for producing bags with sealed edges. In the same way as for the known tube film bags with fin seal, an outward curving of the cross-section of the web is provided for the seam formation. The removal of the web at the fin seal by means of removal rollers is typical for horizontal tubular film bag machines.
Prism shapes with inner angles of greater than 180 degrees, as they are used, for example, in the case of tubes with stabilizing fold, are provided subsequently with additional shaping elements which are provided on the feeding pipe and/or the exterior side of the prism.
For example, folding members are provided below the shaping shoulder within (on the feeding pipe) or outside of the tube which shape the round tube into an angular tube and produce folds thereat (U.S. Pat. No. 5,685,132; DE 196 03 371). This shaping is not planar, i.e., a prism area cut out of this area cannot be developed in a plane. As a result, folds and tears can form in the web or expansions can occur over portions thereof which damage the web.
A further disadvantage of this method is the long shaping path because the shaping shoulder and the fold forming members are positioned sequentially viewed in the transport direction of the tube. This increases the machine size and the product drop height and thus causes damage of the products during the filling process.
A disadvantage of most tubular film bag machines is the technically complex tube removal. The removal force can engage only on the exterior side of the tube, for example, by means of an intermittently moving suction ring or suction belt. For example, friction belts are also employed. In this connection, the different frictional coefficient between a rubberized removal belt and the exterior side of the tube, on the one hand, as well as of a polished shaping pipe and the inner side of the tube, on the other hand, is utilized.
Also known, in general, are machines for shaping a double tube. By means of the shaping shoulder the outer edges of the web are folded such that they meet again at the web center and are then welded to one another or against the web center. In this way, two planar tubes are produced into which flat articles to be packaged, for example, tea bags, can be inserted automatically. However, it is not possible to package articles with great product height in this way. The widening of the tube pair would constitute a non-planar shaping and would result in the above mentioned disadvantages of wrinkle formation or tear formation.
Moreover, generally known is a method of production of several flat bags which move parallel to one another through the machine. In this connection, two webs which move in opposite directions toward one another are welded or sealed with one another in the longitudinal direction upon meeting one another so that a chain of parallel extending tubes arranged transversely to the transport direction or a bag with several chambers separated from one another in the transport direction are formed. The shaping is realized by guiding the web onto flat feeding pipes projecting between the longitudinal welding devices. Shaping is realized in this way in a non-planar fashion. Shaping is possible with avoidance of folds and wrinkles only when the tubes are not opened far. The tubes remain very flat so that they cannot be filled optimally.